COMPOSITION OF CELL-POLYMER CARTILAGE IMPLANTS

Cartilage implants for potential in vivo use for joint repair or reconstructive surgery can be created in vitro by growing chondrocytes on biodegradable polymer scaffolds. Implants 1 cm in diameter by 0.176 cm thick were made using isolated calf chondrocytes and polyglycolic acid (PGA). By 6 weeks, the total amount of glycosaminoglycan (GAG) and collagen (types I and II) increased to 46% of the implant dry weight; there was a corresponding decrease in the mass of PGA. Implant biochemical and histological compositions depended on initial cell density, scaffold thickness, and the methods of cell seeding and implant culture. Implants seeded at higher initial cell densities reached higher GAG contents (total and per cell), presumably due to cooperative cell-to-cell interactions. Thicker implants had lower GAG and collagen contents due to diffusional limitations. Implants that were seeded and cultured under mixed conditions grew to be thicker and more spatially uniform with respect to the distribution of cells, matrix, and remaining polymer than those seeded and/or cultured statically.Implants from mixed cultures had a 20-40-mu m thick superficial zone of flat cells and collagen oriented parallel to the surface and a deep zone with perpendicular columns of cells surrounded by GAG, Mixing during cell seeding and culture resulted in a more even cell distribution and enhanced nutrient diffusion which could be related to a more favorable biomechanical environment for chondrogenesis. Cartilage with appropriate form and function for in vivo implantation can thus be created by selectively stimulating the growth and differentiated function of chondrocytes (i.e., GAG and collagen synthesis) through optimization of the in vitro culture environment. (C) 1994 John Wiley & Sons, Inc.